Ice shed reduction for leading edge structures

ABSTRACT

A leading edge structure for use in an aerospace vehicle includes a body having a flowpath surface which defines a leading edge adapted to face an air flow during operation, and an opposed inner surface. The body is segmented into a plurality of portions having varying thermal properties and/or mechanical discontinuities, so as to promote stress concentrations in ice attached to the flowpath surface.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a Divisional of U.S. patent application Ser. No.12/112,733, filed Apr. 30, 2008, now U.S. Pat. No. 8,245,981.

BACKGROUND OF THE INVENTION

This invention relates generally to aerospace vehicle structures andmore particularly to designs for improving ice shedding characteristicsfrom such structures.

All aircraft include various “leading edge structures”, i.e. exposedsurfaces that face the direction of flight. These surfaces include, forexample, parts of the fuselage, wings, control surfaces, andpowerplants.

One common type of aircraft powerplant is a turbofan engine, whichincludes a turbomachinery core having a high pressure compressor,combustor, and high pressure turbine in serial flow relationship. Thecore is operable in a known manner to generate a flow of propulsive gas.A low pressure turbine driven by the core exhaust gases drives a fanthrough a shaft to generate a propulsive bypass flow. The low pressureturbine also drives a low pressure compressor or “booster” whichsupercharges the inlet flow to the high pressure compressor.

Certain flight conditions allow for ice build up on the leading edgestructures, and in particular the fan and booster flowpath areas of theengine. These areas include the blades, spinner cone, and static vaneand fairing leading edges. The FAA requires certification testing atthese flight points to demonstrate the ability to maintain engine thrustonce the ice sheds from the various components and ingests into theengine.

One particular leading edge structure of interest is the engine's fansplitter. The splitter is an annular ring with an airfoil leading edgethat is positioned immediately aft of the fan blades. Its function is toseparate the airflow for combustion (via the booster) from the bypassairflow. It is desired for the splitter and other leading edgestructures to have mechanical, chemical, and thermal properties suchthat ice build up and shed volume is minimized during an icing event.This in turn minimizes risk of compressor stall and compressormechanical damage from the ingested ice.

Prior art turbofan engines have splitters made from titanium, which isknown to provide favorable ice shed properties. The downside of titaniumis the expense and weight when compared to conventionally treatedaluminum. However, conventionally treated aluminum is believed to behavepoorly in an aircraft icing environment. Examples of conventionallytreated aluminum include but are not limited to chemical conversioncoatings and anodization.

Leading edge structures can also be protected with known coatings thatare referred to as “icephobic” or “anti-ice” coatings, for examplepolyurethane paint or other organic coatings. These coatings have theeffect of lowering adhesion forces between ice accretions and theprotected component. While these coatings can improve ice sheddingcharacteristics, their erosion resistance may be not adequate to protectleading edge structures from the scrubbing effect of airflows withentrained abrasive particles which are encountered in flight.

BRIEF SUMMARY OF THE INVENTION

These and other shortcomings of the prior art are addressed by thepresent invention, which provides components having icephobic platingthat reduces and/or modifies ice adhesion forces to promote ice releaseand reduce shedding of large ice pieces.

According to one aspect, the invention provides a leading edge structurefor use in an aerospace vehicle, including: (a) a body having a flowpathsurface which defines a leading edge adapted to face an air flow duringoperation; and (b) a plurality of mechanical discontinuities formed inthe flowpath surface, the mechanical discontinuities adapted to promotestress concentrations in ice attached to the flowpath surface.

According to another aspect of the invention, a splitter for a turbofanengine includes: (a) an annular body having a flowpath surface whichdefines a leading edge adapted to face an air flow during operation; and(b) a plurality of mechanical discontinuities formed in the flowpathsurface, the mechanical discontinuities adapted to promote stressconcentrations in ice attached to the flowpath surface.

According to another aspect of the invention, a leading edge structurefor use in an aerospace vehicle includes a body having a flowpathsurface which defines a leading edge adapted to face an air flow duringoperation, and an opposed inner surface. The body is segmented into aplurality of portions having varying thermal properties, so as topromote stress concentrations in ice attached to the flowpath surface.

BRIEF DESCRIPTION OF THE DRAWINGS

The invention may be best understood by reference to the followingdescription taken in conjunction with the accompanying drawing figuresin which:

FIG. 1 is a perspective view of an aircraft powered by a pair ofhigh-bypass turbofan engines, incorporating icing-resistant componentsconstructed according to an aspect of the present invention;

FIG. 2 is a schematic half-sectional view of an engine shown in FIG. 1;

FIG. 3 is a half-sectional view of a splitter shown in FIG. 2;

FIG. 4 is a view taken from forward looking aft at the splitter of FIG.3;

FIG. 5 is a view taken along lines 5-5 of FIG. 4;

FIG. 6A is a view taken along lines 6-6 of FIG. 5;

FIG. 6B is a forward looking aft view of a variation of the splitter ofFIG. 6A;

FIG. 7 is a view taken from forward looking aft at an alternativesplitter;

FIG. 8 is a taken along lines 8-8 of FIG. 7;

FIG. 9A is a view taken along lines 9-9 of FIG. 8;

FIG. 9B is a forward looking aft view of a variation of the splitter ofFIG. 9A;

FIG. 10 is a view taken from forward looking aft at another alternativesplitter;

FIG. 11 is a taken along lines 11-11 of FIG. 10;

FIG. 12A is a view taken along lines 12-12 of FIG. 11; and

FIG. 12B is a forward looking aft view of a variation of the splitter ofFIG. 12A

DETAILED DESCRIPTION OF THE INVENTION

Referring to the drawings wherein identical reference numerals denotethe same elements throughout the various views, FIG. 1 depicts a knowntype of commercial aircraft 10 which includes a generally tubularfuselage 12, wings 14 carrying turbofan engines 16 mounted in nacelles18, and an empennage comprising horizontal and vertical stabilizers 20and 22. Each of these components includes one or more exposed surfaceshaving a curved or airfoil-like cross-section that faces the directionof flight (in other words an aerodynamic leading edge). These surfacesare referred to herein as “leading edge structures”. While the presentinvention will be described further in the context of a gas turbineengine, it will be understood that the principles contained therein maybe applied to any type of leading edge structure.

As shown in FIG. 2, the engine 16 has a longitudinal axis “A” andincludes conventional components including a fan 24, a low pressurecompressor or “booster” 26 and a low pressure turbine (“LPT”) 28,collectively referred to as a “low pressure system”, and a high pressurecompressor (“HPC”) 30, a combustor 32, and a high pressure turbine(“HPT”) 34, collectively referred to as a “gas generator” or “core”.Various components of the nacelle 18 and stationary structures of theengine 16, including a core nacelle 36, cooperate to define a coreflowpath marked with an arrow “F”, and a bypass duct marked with anarrow “B”.

A stationary annular splitter 38 (also seen in FIG. 3) is positioned atthe forward end of the core nacelle 36, between the bypass duct B andthe core flowpath F. The flowpath surface 40 of the splitter 38 includesa radially-outward-facing portion 41 and a radially-inward-facingportion 43. The two portions are demarcated by an aerodynamic leadingedge 39. An inner surface 45, not exposed to the primary flowpath, isdisposed opposite the flowpath surface 40. The splitter 38 is an exampleof a leading edge structure as described above. The splitter 38 may be asingle continuous ring, or it may be built up from arcuate segments.

The flowpath surface 40 includes one or more discontinuities for thepurpose of improving ice shed characteristics. As shown in FIGS. 3-6A,the splitter 38 has a radial array of generally axially aligned grooves42 formed therein. As an example, the width “W” of the grooves may befrom as small as about 0.38 mm (0.015 in.) up to as large as 50% of thecircumference of the splitter 38. FIG. 6B illustrates a slightlydifferent splitter 38′ in which the flowpath surface 40′ has grooves 42′that are curved. They may be curved so as to be parallel to the localflowfield during operation. FIGS. 7-9A illustrate an alternativesplitter 138 that has a radial array of generally axially aligned,raised ribs 142 protruding from its flowpath surface 140. The spacing“S” of the grooves 42 or ribs 142 in the circumferential direction maybe selected to cause ice to breakup into relatively small pieces. As anexample, about 24 to about 140 features distributed around thecircumference are believed to be suitable for this purpose. FIG. 9Billustrates a slightly different splitter 138′ in which the flowpathsurface 140′ has ribs 142′ that are curved. They may be curved so as tobe parallel to the local flowfield during operation. Various patterns ofgrooves or ribs running in different directions (axial, circumferential,and combinations of each direction etc.) may be used.

FIGS. 10-12A illustrate another alternative splitter 238 whose flowpathsurface 240 includes alternating sections 242A and 242B havingsubstantially different thicknesses such that adjacent sections areoffset in a direction normal to the flowpath surface (i.e. in the radialdirection in illustrated example). The delineations between adjacentsections 242A and 242B present generally radially aligned faces 244which act as discontinuities in the flowpath surface 240. FIG. 12Billustrates a slightly different splitter 238′ in which the flowpathsurface comprises segments 242′ that are tapered in thickness in thecircumferential direction. The delineations between adjacent sections242′ present generally radially curved faces 244′ which act asdiscontinuities. The faces 244′ may be curved so as to be parallel tothe local flowfield during operation. As with the grooves or ribs, thedelineations may be implemented in various patterns running in differentdirections (axial, circumferential, etc.)

In operation, the engine 10 will be exposed to icing conditions, namelythe presence of moisture in temperatures near the freezing point ofwater. Ice will naturally tend to form on the leading edge structuresincluding the splitter 38. As the ice mass builds up, it protrudes intothe air flow and increasing aerodynamic (drag) forces act on it,eventually causing portions of it to shed from the splitter 38. Thepresence of the discontinuities described above promotes stressconcentrations and introduces mechanical stresses into the ice. Theresult is that pieces of the ice break off and shed downstream when theyare a smaller size than would otherwise be the case. This avoidsexcessive cooling and foreign object damage in the high pressurecompressor 30.

In addition to, or as an alternative to the techniques described above,the thermal properties of the leading edge structure can be varied bychanges in either alloy type or thickness. Changes to surface propertiesand texture may also help with heat transfer. Also, the internal(non-flowpath) surfaces can be varied in order to achieve the desiredthermal variations. For example, the local thickness variation describedabove can be achieved by adding thickness to the inner surface, whileleaving the flowpath surface unchanged).

The foregoing has described aerospace structures adapted for improvedice shedding characteristics. While specific embodiments of the presentinvention have been described, it will be apparent to those skilled inthe art that various modifications thereto can be made without departingfrom the spirit and scope of the invention. Accordingly, the foregoingdescription of the preferred embodiment of the invention and the bestmode for practicing the invention are provided for the purpose ofillustration only.

1. A leading edge structure for use in an aerospace vehicle, comprising:(a) a body having a flowpath surface which defines a leading edgeadapted to face an air flow during operation; and (b) a plurality ofmechanical discontinuities formed in the flowpath surface, themechanical discontinuities adapted to promote stress concentrations inice attached to the flowpath surface.
 2. The leading edge structure ofclaim 1 wherein the discontinuities are defined by one or more ribsextending from the flowpath surface.
 3. The leading edge structure ofclaim 2 wherein the ribs are curved so as to be generally parallel tothe expected flowfield around the flowpath surface during operation. 4.The leading edge structure of claim 1 wherein the discontinuities aredefined by adjacent portions of the flowpath surface which are offsetfrom each other.
 5. The leading edge structure of claim 4 wherein facesdefined by adjacent portions of the flowpath surface are curved so as tobe generally parallel to the expected flowfield around the flowpathsurface during operation.
 6. The leading edge structure of claim 1wherein the body comprises aluminum.
 7. A splitter for a turbofanengine, comprising: (a) an annular body having a flowpath surface whichdefines a leading edge adapted to face an air flow during operation; and(b) a plurality of mechanical discontinuities formed in the flowpathsurface, the mechanical discontinuities adapted to promote stressconcentrations in ice attached to the flowpath surface.
 8. The splitterof claim 7 wherein the discontinuities are defined by one or more ribsextending from the flowpath surface.
 9. The splitter of claim 8 whereinthe ribs are curved so as to be generally parallel to the expectedflowfield around the flowpath surface during operation.
 10. The splitterof claim 8 wherein the flowpath surface has a radial array of generallyaxially-aligned ribs protruding therefrom.
 11. The splitter of claim 7wherein the discontinuities are defined by adjacent portions of theflowpath surface which are offset from each other.
 12. The splitter ofclaim 11 wherein faces defined by adjacent portions of the flowpathsurface are curved so as to be generally parallel to the expectedflowfield around the flowpath surface during operation.
 13. The splitterof claim 7 wherein the body comprises aluminum.
 14. A leading edgestructure for use in an aerospace vehicle, comprising a body having aflowpath surface which defines a leading edge adapted to face an airflow during operation, and an opposed inner surface; wherein the body issegmented into a plurality of portions having varying thermalproperties, so as to promote stress concentrations in ice attached tothe flowpath surface.
 15. The leading edge structure of claim 14 whereinadjacent portions of the body have different thicknesses.
 16. Theleading edge structure of claim 15 wherein the flowpath surface issubstantially free from discontinuities.
 17. The leading edge structureof claim 14 wherein adjacent portions of the body are constructed ofdifferent alloys.
 18. The leading edge structure of claim 14 whereinadjacent portions of the body have different surface textures of theflowpath surface.